Fuel injection valve

ABSTRACT

A stem is installed to an injector body and is resiliently deformable upon receiving a pressure of high pressure fuel conducted through a high pressure passage of the injector body. A strain gauge is installed to the stem to sense a strain generated in the stem. A molded IC device executes an amplifying operation, which amplifies a signal received from the strain gauge. A housing is installed to the stem and holds the molded IC device. The stem, the strain gauge the molded IC device and the housing are integrally assembled together to form a fuel pressure sensing unit, which is installed to the injector body by threadably fastening a threaded portion, which is formed at the housing, to the injector body.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by referenceJapanese Patent Application No. 2009-90738 filed on Apr. 3, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel injection valve, which isinstalled to an internal combustion engine and injects fuel through aninjection hole thereof.

2. Description of Related Art

In order to accurately control an output torque and an emission state ofan internal combustion engine, it is important to accurately control aninjection state of a fuel injection valve (e.g., start timing of fuelinjection at the fuel injection valve and the amount of fuel injectedfrom the fuel injection valve). In view of the above point, there hasbeen proposed a technique for sensing an actual injection state bysensing a pressure of fuel, which changes in response to fuel injection.For example, the actual start timing of the fuel injection may be sensedby sensing the start timing of decreasing of the fuel pressure caused bythe start of the fuel injection, and the actual end timing of the fuelinjection may be sensed by sensing the stop timing of increasing of thefuel pressure caused by the termination of the fuel injection (see, forexample, Japanese Unexamined Patent Publication No. 2008-144749Acorresponding to US 2008/0228374A1).

When a fuel pressure sensor (rail pressure sensor), which is directlyinstalled to a common rail (accumulator), is used to sense the change inthe fuel pressure, accurate measurement of the change in the fuelpressure is difficult since the change in the fuel pressure caused bythe fuel injection is buffered in the common rail. In the case of theinvention recited in Japanese Unexamined Patent Publication No.2008-144749A, the fuel pressure sensor is installed to the fuelinjection valve to sense the change in the fuel pressure caused by thefuel injection before the change in the fuel pressure is buffered in thecommon rail.

In the above fuel injection valve, a body has a high pressure passage,which conducts high pressure fuel to the injection hole. The bodyreceives a needle and an actuator. The needle is reciprocated away fromor toward the injection hole to open or close the injection hole, andthe actuator drives the needle. The inventors of the present applicationhave previously proposed to install a fuel pressure sensor, which isconstructed in the following manner, to the body. Specifically, the fuelpressure sensor includes a flexure element, a sensor element and asignal processing circuit. The flexure element is installed to the bodyand is adapted to be resiliently deformed upon application of thepressure of the high pressure fuel to the flexure element. The sensorelement converts the strain, which is generated in the flexure element,into a corresponding electrical signal. The signal processing circuitperforms, for example, an amplifying operation, which amplifies themeasurement signal outputted from the sensor element.

Prior to shipment of the injector to a market, various tests andinspections need to be performed on the fuel pressure sensor. Thesetests and inspections will be described below.

A thermal expansion deformation of the flexure element is increased whenthe fuel temperature is increased. Therefore, the output value of thefuel pressure sensor (i.e., the sensor output value, which is outputtedfrom the signal processing circuit) is drifted. Thereby, the fuelpressure needs to be computed based on the sensor output value in viewof the amount of the temperature drift discussed above. The amount ofthe temperature drift may be a flexure element specific value, which mayvary from one flexure element to another flexure element. Therefore, theamount of the temperature drift needs to be obtained in advance throughexperiments (temperature characteristic test) before shipment of thefuel injection valve to the market.

Thereby, in an assembled state, in which the flexure element, the sensorelement and the signal processing circuit are installed to the body,fuel, which is under a test temperature and a test pressure, is suppliedto the high pressure passage of the body to apply the pressure of thefuel to the flexure element. The amount of the temperature drift forthis specific test temperature is obtained based on the sensor outputvalue, the test pressure and test temperature of the fuel at this testtime. Furthermore, an abnormality inspection of the fuel pressure sensoris performed by checking whether the sensor output value, which isobtained for the specific test pressure, is out of a normal range.

In the installed state, in which the flexure element is installed to thebody, the temperature of the flexure element and the temperature of thebody need to be stabilized to the test temperature. However, a thermalmass (also called thermal capacitance or heat capacity) of the body isrelatively large. Therefore, an extra time is required to stabilize thetemperature of the body to the test temperature. Furthermore, when theabnormality is detected in the abnormality inspection, which isperformed on the fuel injection valve in the assembled state where thefuel pressure sensor is installed to the body, the entire fuel injectionvalve needs to be handled as an abnormal product. Thereby, it causes areduction in the manufacturing yield of the fuel injection valve.

SUMMARY OF THE INVENTION

The present invention is made in view of the above disadvantage.According to the present invention, there is provided a fuel injectionvalve being adapted to be installed to an internal combustion engine andhaving an injection hole to inject fuel therethrough. The fuel injectionvalve includes a body, a flexure element, a sensor element, a signalprocessing circuit and a holding member. The body includes a highpressure passage, which is adapted to conduct high pressure fuel towardthe injection hole. The flexure element is installed to the body and isresiliently deformable upon receiving a pressure of the high pressurefuel conducted through the high pressure passage. The sensor element isinstalled to the flexure element to sense a strain generated in theflexure element. The sensor element converts the sensed strain into acorresponding electrical signal. The signal processing circuit executesat least an amplifying operation, which amplifies the signal receivedfrom the sensor element. The holding member is installed to the flexureelement and holds the signal processing circuit. The flexure element,the sensor element, the signal processing circuit and the holding memberare integrally assembled together to form a fuel pressure sensing unit.The fuel pressure sensing unit is installed to the body by threadablyfastening a threaded portion, which is formed at the holding member, tothe body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of an injector according to afirst embodiment of the present invention, schematically showing aninternal structure of the injector;

FIG. 2 is an enlarged partial cross-sectional view of the injector ofFIG. 1, showing an area around a fuel pressure sensor of the injector;

FIG. 3 is an enlarged cross-sectional view of a fuel pressure sensingunit, which is removed from an injector body of the injector of FIG. 1;

FIG. 4A is a top view showing the housing installed to the stemaccording to the first embodiment;

FIG. 4B is a top view showing a housing installed to a stem according toa second embodiment of the present invention;

FIG. 4C is a top view showing a modification of the second embodimentshown in FIG. 4B;

FIG. 5A is a cross-sectional view showing a fuel pressure sensing unitaccording to a third embodiment of the present invention; and

FIG. 5B is a cross-sectional view showing a modification of the thirdembodiment shown in FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be described withreference to the accompanying drawings. In the following description,similar components will be indicated by the same reference numeralsthroughout the embodiments, and these similar components, which arediscussed in the first embodiment, will not be described redundantly inthe other embodiments for the sake of simplicity.

First Embodiment

The first embodiment of the present invention will be described withreference to FIGS. 1 to 3 and 4A. FIG. 1 is a cross-sectional view of aninjector (fuel injection valve) of the present embodiment, schematicallyshowing a structure of the injector. A basic structure and operation ofthe injector will be described with reference to FIG. 1.

The injector receives high pressure fuel stored in an undepicted commonrail (accumulator) and injects the received high pressure fuel into acombustion chamber E1 that is defined in a corresponding cylinder of adiesel engine (internal combustion engine). The injector includes anozzle 1, an electric actuator (drive means) 2 and a back pressurecontrol mechanism 3. The nozzle 1 is provided to inject fuel therefromat the valve opening time (i.e., the time of opening an injection holeof the injector to inject fuel). The electric actuator 2 is driven uponreceiving electric power. The back pressure control mechanism 3 isdriven by the electric actuator 2 to control the back pressure of thenozzle 1.

The nozzle 1 includes a nozzle body 12, a needle 13 and a spring 14. Theinjection hole 11 is formed through a wall of the nozzle body 12. Theneedle 13 is adapted to axially reciprocate away from and toward a valveseat of the nozzle body 12 to open and close the injection hole 11. Thespring 14 urges the needle 13 in a valve closing direction (directiontoward the valve seat and the injection hole 11 of the nozzle body 12).

The electric actuator 2 is a piezoelectric actuator, which includes aplurality of piezoelectric elements that are stacked one after anotherto form a piezoelectric stack. When the piezoelectric elements of thepiezoelectric stack are electrically charged or discharged, thepiezoelectric stack is expanded or contracted, respectively. In thisway, the piezoelectric stack functions as the actuator that drives theneedle 13. In place of the piezoelectric actuator, a solenoid actuator,which includes a stator and an armature, may be used.

The valve body 31 of the back pressure control mechanism 3 receives apiston 32, a Belleville spring 33 and a valve element 34. The piston 32is driven in response to the expansion or contraction of thepiezoelectric actuator 2. The Belleville spring 33 urges the piston 32toward the piezoelectric actuator 2. The valve element 34 is configuredinto a spherical body and is driven by the piston 32.

An injector body 4, which is configured into a generally cylindricaltubular body, has a receiving hole 41, which is configured into astepped cylindrical hole that extends in an axial direction of theinjector (top-to-bottom direction in FIG. 1). The piezoelectric actuator2 and the back pressure control mechanism 3 are received in thereceiving hole 41. A retainer 5, which is configured into a generallycylindrical tubular body, is threadably engaged with the injector body4, so that the nozzle 1 is securely held at a distal end part of theinjector body 4.

A high pressure passage 6 and a low pressure passage 7 are formed in thenozzle body 12, the injector body 4 and the valve body 31. The highpressure fuel is always supplied from the common rail to the highpressure passage 6, and the low pressure passage 7 is connected to afuel tank (not shown). Each of the nozzle body 12, the injector body 4and the valve body 31 is made of metal and is hardened through aquenching process. Furthermore, the surface of each of the nozzle body12, the injector body 4 and the valve body 31 is hardened through acarburization process (carbonitriding process).

The nozzle body 12, the injector body 4 and the valve body 31 areinserted into an insertion hole E3, which is formed in a cylinder headE2 of the engine. The injector body 4 has an engaging portion 42, whichis engaged with one end part of a clamp K. A bolt, which is received ina through hole of the other end part of the clamp K, is threadablytightened into a corresponding bolt hole, which is formed in the toppart of the cylinder head E2, so that the other end part of the clamp Kis urged against the cylinder head E2, and thereby the one end part ofthe clamp K urges the engaging portion 42 into the insertion hole E3.Thus, the injector is secured while being urged into the insertion holeE3.

A high pressure chamber 15, which forms a part of the high pressurepassage 6, is formed between an outer peripheral surface of a distal endpart of the needle 13, which is placed adjacent to the injection hole11, and an inner peripheral surface of the nozzle body 12. The highpressure chamber 15 is communicated with the injection hole 11 when theneedle 13 is displaced in a valve opening direction (direction away fromthe valve seat and the injection hole 11). A back pressure chamber 16 isformed on the other axial side of the needle 13, which is opposite fromthe injection hole 11. The spring 14 is placed in the back pressurechamber 16.

The valve body 31 has a high pressure seat surface 35 and a low pressureseat surface 36. The high pressure seat surface 35 is formed in apassage, which communicates between the high pressure passage 6 in thevalve body 31 and the back pressure chamber 16 of the nozzle 1. The lowpressure seat surface 36 is formed in a passage, which communicatesbetween the low pressure passage 7 in the valve body 31 and the backpressure chamber 16 of the nozzle 1. The valve element 34 is placedbetween the high pressure seat surface 35 and the low pressure seatsurface 36.

The injector body 4 has a high pressure port (high pressure conduitconnecting portion) 43, which is connected to an undepicted highpressure conduit, and a low pressure port (low pressure conduitconnecting portion) 44, which is connected to an undepicted low pressureconduit. The fuel, which is received from the common rail through thehigh pressure conduit, is supplied to the high pressure port 43 of theinjector body 4 from the outer peripheral surface side thereof. Thefuel, which is supplied to the injector, flows into the high pressurechamber 15 and the back pressure chamber 16 through the high pressurepassage 6.

A branch passage 6 a is branched from the high pressure passage 6 in theother axial direction, which is opposite from the injection hole 11 inthe injector body 4. The branch passage 6 a conducts the fuel from thehigh pressure passage 6 to a fuel pressure sensor 50, which will bedescribed later in detail. The branch passage 6 a may possibly serve asa part of the high pressure passage 6.

A connector 60 is installed to a top part of the injector body 4, whichis located on the other axial side that is opposite from the injectionhole 11. The electric power, which is supplied from an external powersource to a terminal (a drive connector terminal 62) of the connector60, is supplied to the piezoelectric actuator 2 through a lead line(conductive line) 21. When the electric power is supplied to thepiezoelectric actuator 2 through the terminal of the connector 60, thepiezoelectric actuator 2 is expanded. In contrast, when the supply ofthe electric power to the piezoelectric actuator 2 is stopped, thepiezoelectric actuator 2 is contracted.

In the contracted state of the piezoelectric actuator 2, as shown inFIG. 1, the valve element 34 is engaged with the low pressure seatsurface 36. Therefore, the back pressure chamber 16 is communicated withthe high pressure passage 6, and thereby the high fuel pressure isguided into the back pressure chamber 16. The fuel pressure in the backpressure chamber 16 and the urging force of the spring 14 urge theneedle 13 in the valve closing direction, so that the injection hole 11is closed.

In contrast, in the expanded state of the piezoelectric actuator 2,which is achieved by applying the voltage to the piezoelectric actuator2, the valve element 34 is engaged with the high pressure seat surface35. Therefore, the back pressure chamber 16 is communicated with the lowpressure passage 7, and thereby the pressure of the back pressurechamber 16 is reduced to the low pressure. The fuel pressure in the highpressure chamber 15 urges the needle 13 in the valve opening direction,so that the injection hole 11 is opened to inject the fuel into thecombustion chamber E1 through the injection hole 11.

When the fuel is injected through the injection hole 11, the pressure ofthe high pressure fuel in the high pressure passage 6 is changed. Thefuel pressure sensor 50, which senses this pressure change, is installedto the injector body 4. The timing, at which the fuel pressure begins todecrease due to the start of the fuel injection through the injectionhole 11, is sensed by monitoring a waveform, which indicates themeasured pressure change that is measured with the fuel pressure sensor50. In this way, the actual start timing of the fuel injection can besensed. Furthermore, the timing, at which the fuel pressure begins toincrease due to the termination of the fuel injection through theinjection hole 11, is sensed. In this way, the actual end timing of thefuel injection can be sensed. Furthermore, in addition to the starttiming and the end timing of the fuel injection, the maximum value ofthe fuel pressure decrease, which is caused by the fuel injection, issensed. In this way, the amount of fuel injected through the injectionhole 11 can be sensed.

Next, the structure of the fuel pressure sensor 50 and the structure forinstalling the fuel pressure sensor 50 to the injector body 4 will bedescribed with reference to FIGS. 2 and 3. FIG. 2 is an enlarged view ofFIG. 1, and FIG. 3 is a cross-sectional view of a fuel pressure sensingunit shown in FIG. 2.

The fuel pressure sensor 50 includes a stem (flexure element) 51 and astrain gauge (sensor element) 52. The stem 51 is resiliently deformableupon application of the pressure of the high pressure fuel in the branchpassage 6 a. The strain gauge 52 senses the strain (the amount of thestrain), which is generated in the stem 51, and converts the sensedstrain into a corresponding electrical signal, and this electricalsignal is outputted from the strain gauge 52 as a pressure measurementvalue.

The stem 51 is configured into a generally cylindrical hollow bodyhaving a flow inlet 51 a at one axial end part thereof and a closedbottom at the other axial end part thereof. More specifically, the stem51 includes a cylindrical tubular portion 51 b and a diaphragm 51 c. Thecylindrical tubular portion 51 b has the flow inlet 51 a at one axialend part (cylindrical tubular end part) thereof to receive the highpressure fuel therethrough. The diaphragm 51 c is configured into acircular disk body that closes the other axial end part of thecylindrical tubular portion 51 b. The pressure of the high pressurefuel, which is supplied into the interior of the cylindrical tubularportion 51 b through the flow inlet 51 a, is applied to an innerperipheral surface of the cylindrical tubular portion 51 b and thediaphragm 51 c. In this way, the entire stem 51 is resiliently deformed.

The stem 51 is made of a metal material. Since the stem 51 receives thevery high pressure, the metal material of the stem 51 needs to have ahigh strength and a high hardness. Furthermore, the amount ofdeformation of the metal material of the stem 51 caused by thermalexpansion thereof needs be small to have a small influence on the straingauge 52. That is, the metal material of the stem 51 needs to have asmall coefficient of thermal expansion. Specifically, the metal materialof the stem 51 may be an alloy that includes, for instance, iron (Fe),nickel (Ni) and cobalt (Co) or alternatively iron (Fe) and nickel (Ni)as its main components and further include titanium (Ti), niobium (Nb)and aluminum (Al) or alternatively titanium (Ti) and niobium (Nb) as itsprecipitation-hardening components. The metal material may be configuredinto the above described shape of the stem 51 by press-working, cuttingor cold forging. Furthermore, the material, into which, for example,carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and/or sulfur(S) are added, may be used as the material of the stem 51.

A recess 45 is formed in an end surface at the other axial end part ofthe injector body 4, which is opposite from the injection hole 11. Thecylindrical tubular portion 51 b of the stem 51 is received in therecess 45. A sensor side seal surface 51 e is formed around the flowinlet 51 a in an end surface at the one axial end part of thecylindrical tubular portion 51 b. A body side seal surface 45 b isformed in a bottom surface of the recess 45. The sensor side sealsurface 51 e and the body side seal surface 45 b are annular around theflow inlet 51 a and extend in a plane that is perpendicular to the axialdirection (top-to-bottom direction in FIG. 2) of the stem 51. The sensorside seal surface 51 e is tightly urged against the body side sealsurface 45 b to form a metal-to-metal seal (also referred to as a metaltouch seal) between the injector body 4 and the stem 51.

The strain gauge 52 is installed to the outer surface (top surface) thediaphragm 51 c. Specifically, the strain gauge 52 is fixed byencapsulating the strain gauge 52 with a glass member 52 b through useof a heating technique, which heats a glass material of the glass member52 b to encapsulate the strain gauge 52. When the stem 51 is resilientlydeformed, i.e., is resiliently expanded by the pressure of the highpressure fuel supplied into the interior of the cylindrical tubularportion 51 b, the amount of strain (the amount of resilient deformation)generated on the diaphragm 51 c is sensed with the strain gauge 52.

A housing (holding member) 53, which is made of a metal material, isinstalled to the stem 51. The housing 53 includes an IC holding portion(receiving portion) 53 a, a cylindrical tubular portion (cylindricaltubular portion of the holding member) 53 c and tool engaging portions(receiving portions) 53 d, which will be described below. The IC holdingportion 53 a is a generally circular disk body and is supported by thecylindrical tubular portion 51 b of the stem 51. Furthermore, an outerdiameter of the IC holding portion 53 a is larger than the outerdiameter of the cylindrical tubular portion 51 b of the stem 51.

An insertion hole 53 b is formed in the IC holding portion 53 a, and thecylindrical tubular portion 51 b of the stem 51 is inserted into theinsertion hole 53 b. When the cylindrical tubular portion 51 b isinserted into the insertion hole 53 b from the injector body 4 side, thestrain gauge 52 is disposed in the interior of the housing 53.

The cylindrical tubular portion 53 c of the housing 53 axially projectsfrom an end of the insertion hole 53 b (an end surface, i.e., an outerbottom surface of the IC holding portion 53 a). The cylindrical tubularportion 53 c of the housing 53 is configured into a generallycylindrical tubular body that is engaged with and extends along an outerperipheral surface of the cylindrical tubular portion 51 b of the stem51, and the IC holding portion 53 a radially outwardly projects from theouter peripheral surface of the proximal end part of the cylindricaltubular portion 53 c, at which the insertion hole 53 b is formed. Thecylindrical tubular portion 51 b of the stem 51 is press fitted to aninner peripheral surface of the cylindrical tubular portion 53 c of thehousing 53. FIG. 4A is a top view showing the housing 53 and the stem 51upon the insertion of the cylindrical tubular portion 51 b of the stem51 into the cylindrical tubular portion 53 c of the housing 53 seen fromthe side of the housing 53, which is opposite from the stem 51. In thepresent embodiment, as shown in FIG. 4A, two planar fitting surfaceportions 531 b, which are generally parallel to each other and arediametrically opposed to each other, are formed in the inner peripheralsurface of the cylindrical tubular portion 53 c of the housing 53. Twoplanar fitting surface portions 51 g, which are generally parallel toeach other and are diametrically opposed to each other, are formed atthe outer peripheral surface of the section of the cylindrical tubularportion 51 b, which is adjacent to the diaphragm 51 c. These fittingsurface portions 51 g of the cylindrical tubular portion 51 b are pressfitted between the fitting surface portions 531 b of the cylindricaltubular portion 53 c of the housing 53. When the fitting surfaceportions 531 b are press fitted against the fitting surface portions 51g, the housing 53 is installed to the stem 51 and is held non-rotatablyrelative to the stem 51, i.e., the housing 53 is non-rotatably installedto the stem 51.

The cylindrical tubular portion 53 c of the housing 53, which holds thecylindrical tubular portion 51 b of the stern 51, is inserted into therecess 45 of the injector body 4. A male threaded portion (sensor sidethreaded portion) 53 e is formed in an outer peripheral surface of thecylindrical tubular portion 53 c of the housing 53, and a femalethreaded portion (body side threaded portion) 45 a is formed in an innerperipheral surface of the recess 45. When the male threaded portion 53 eof the housing 53 is threadably fastened to the female threaded portion45 a of the injector body 4, the fuel pressure sensor 50 is installed tothe injector body 4.

In the stem 51, an outer diameter of the one axial end part of thecylindrical tubular portion 51 b, at which the sensor side seal surface51 e is formed, is larger than an outer diameter of the other axial endpart of the cylindrical tubular portion 51 b, at which the diaphragm 51c is formed. A step (annular flange) 51 f is formed in the outerperipheral surface of the cylindrical tubular portion 51 b due to thediameter difference described above, and a bottom end surface of thecylindrical tubular portion 53 c of the housing 53 axially abuts againsta top surface of the step 51 f. Therefore, when the male threadedportion 53 e of the housing 53 is threadably fastened to the femalethreaded portion 45 a of the injector body 4, the bottom end surface ofthe cylindrical tubular portion 53 c of the housing 53 is axially urgedagainst the top surface of the step 51 f. The urging force (axialforce), which urges the sensor side seal surface 51 e and the body sideseal surface 45 b toward each other, is generated by fastening the stem51 to the injector body 4 through the thread engagement between the malethreaded portion 53 e of the housing 53 and the female threaded portion45 a of the injector body 4. Specifically, the installation of the fuelpressure sensing unit U to the injector body 4 and the generation of theaxial force are simultaneously performed.

The tool engaging portions 53 d are placed one after another along theouter peripheral edge of the IC holding portion 53 a to engage with anundepicted rotary fastening tool (e.g., a spanner). Specifically, aplurality of fitting surface portions, which radially outwardly projectfrom the outer peripheral edge of the IC holding portion 53 a, are bentin the axially direction to axially project toward the side oppositefrom the injector body 4 to form the tool engaging portions 53 d. In thecase of FIGS. 3 and 4A, the number of the tool engaging portions 53 d issix to form a hexahedron when viewed from the top side or bottom side. Adistance between the diametrically opposed two of the fitting surfaceportions, i.e., the tool engaging portions 53 d is larger than the outerdiameter of the cylindrical tubular portion 53 c of the housing 53.Here, it should be noted that the tool engaging portions 53 d may becollectively referred to as a tool engaging portion. Furthermore, thetool engaging portions 53 d may be replaced with a single tool engagingportion which is continuously formed along the generally hexagonal outerperipheral edge of the IC holding portion 53 a, if desired.

Therefore, when the tool is engaged with the tool engaging portions 53 dand is rotated to rotate the housing 53, the male threaded portion 53 eof the housing 53 is threadably fastened into the female threadedportion 45 a of the injector body 4. Thereby, the fuel pressure sensingunit U is installed to the injector body 4. The housing 53 isnon-rotatably installed to the stem 51. Therefore, the housing 53 can berotated with the tool while maintaining the electrically connected stateof the molded IC device 54 and the strain gauge 52, in which the moldedIC device 54 and the strain gauge 52 are electrically connected witheach other through wires W.

A molded integrated circuit (IC) device 54, which has a signalprocessing circuit, is supported on the IC holding portion 53 a througha spacer 57. The molded IC device 54 is electrically connected to thestrain gauge 52 through the wires W at a wire bonding process. Themolded IC device 54 includes an electronic component 54 a and sensorterminals 54 b, which are held in the mold resin 54 m by, for example,encapsulation.

The spacer 57 is provided to adjust the axial level (height) of themolded IC device 54 such that a wire bonding location of the molded ICdevice 54 and a wire bonding location of the strain gauge 52 are placedgenerally on the common plane. When the spacer 57 is made of a resinmaterial, the spacer 57 can function as a heat insulator to limitconduction of heat from the injector body 4 to the molded IC device 54through the stem 51 and the housing 53 and thereby to limit a thermaldamage of the molded IC device 54.

The electronic component 54 a has, for example, an amplifier circuit foramplifying the measurement signal outputted from the strain gauge 52, afiltering circuit for filtering noises overlapped on the measurementsignal outputted from the strain gauge 52, and a voltage applyingcircuit for applying an electric voltage to the strain gauge 52.

The strain gauge 52, to which the electric voltage is applied from thevoltage applying circuit, has a bridge circuit, at which a value ofelectric resistance is changed in response to the amount of straingenerated in the diaphragm 51 c. In this way, the output voltage of thebridge circuit of the strain gauge 52 is changed in response to theamount of strain of the diaphragm 51 c, and the output voltage of thebridge circuit is outputted from the strain gauge 52 to the amplifiercircuit of the molded IC device 54 as the pressure measurement value,which indicates the pressure of the high pressure fuel. The amplifiercircuit amplifies the pressure measurement value, which is outputtedfrom the strain gauge 52 (more specifically, the bridge circuit of thestrain gauge 52), and the amplified signal is outputted from the moldedIC device 54 through a corresponding one of the sensor terminals 54 b.

The mold resin 54 m is configured into a cylindrical tubular body, whichextends along the outer peripheral surface of the cylindrical tubularportion 51 b of the stem 51. The sensor terminals 54 b project out fromthe mold resin 54 m. The sensor terminals 54 b are electricallyconnected to the electronic component 54 a in the interior of the moldedIC device 54 and include, for example, the terminal for outputting themeasurement signal of the fuel pressure sensor, the terminal forsupplying the electric power, and the ground terminal connected to aground.

A case 56, which is made of a metal material, is installed to the toolengaging portions 53 d of the housing 53. The strain gauge 52 and themolded IC device 54 and a remaining part of the cylindrical tubularportion 51 b of the stem 51, which is other than the one end part of thecylindrical tubular portion 51 b including the step (flange) 51 f, arereceived in the interior of the case 56 and the housing 53. In this way,the metal case 56 and the metal housing 53 shield the external noises toprotect the strain gauge 52 and the molded IC device 54 from theexternal noises. An opening 56 a is formed in the case 56, and thesensor terminals 54 b extend from the interior to the exterior of thecase 56 through the opening 56 a.

Referring back to FIG. 2, the housing 61 of the connector 60 holds driveconnector terminals 62 and sensor connector terminals 63. The sensorconnector terminals 63 are electrically connected to the sensorterminals 54 b through electrodes 71-74 described later by, for example,laser welding. The connector 60 is adapted to connect with a connectorof an external harness, which is connected to an external device, suchas an undepicted engine electronic control unit (ECU). In this way, thepressure measurement signal, which is outputted from the molded ICdevice 54, is supplied to the engine ECU through the external harness.

Here, in the threadably fastening operation of the housing 53, whichsecurely holds the stem 51, to the injector body 4 performed by rotatingthe housing 53 relative to the injector body 4 to threadably engage themale threaded portion 53 e with the female threaded portion 45 a, thefinal rotational position of the housing 53 and the stem 51 at the endof the threadably fastening operation cannot be fixed to any particularposition. Therefore, the final rotational position of the housing 53 andthe stem 51 is indefinite. It means that a final rotational position ofeach of the sensor terminals 54 b of the molded IC device 54 at the endof the threadably fastening operation of the housing 53 is indefinite.

In view of the above matter, each of the electrodes 72-74, which areconnected to the sensor terminals 54 b, respectively, and are rotatedalong with the housing 53 and the stem 51, has an annular connection 72a-74 a, which is annular like a ring in an imaginary plane perpendicularto the rotational axis (the axial direction) of the housing 53 and thestem 51 and circumferentially extends about the rotational axis of thehousing 53 and the stem 51. The annular connections 72 a-74 a areelectrically connected to the sensor connector terminals 63,respectively, after completion of the threadably fastening operation ofthe housing 53. In this way, each of the sensor terminals 54 b, thefinal rotational position of which is not definite, can be easilyelectrically connected to the corresponding one of the sensor connectorterminals 63, which is placed at a predetermined position of theinjector body 4.

A connection 71 a of the electrode 71, which is electrically connectedto the corresponding connector terminal 63, is placed at the rotationalcenter (rotational axis) of the housing 53 and the stem 51. Therefore,the final rotational position of the connection 71 a of the electrode 71at the end of the threadably fastening operation of the housing 53 isdefinite regardless of the rotational position of the housing 53 and thestem 51. The electrodes 71-74 are integrally insert molded in the moldresin 70 m and are placed on the top surface of the case 56 in thismolded state. Each of the sensor connector terminals 63 has a weldingportion (semispherical portion) 63 a, which projects toward thecorresponding one of the connections 71 a-74 a. The laser energy at thetime of the laser welding is concentrated at the welding portion 63 a.

The fuel pressure sensor 50 (including the stem 51 and the strain gauge52), the housing 53, the molded IC device 54, the case 56, the spacer 57and the electrode 71 are integrally assembled as a unit, morespecifically the fuel pressure sensing unit U. FIG. 3 is across-sectional view showing the fuel pressure sensing unit U, which isassembled in the above described manner. When the housing 53 isthreadably fastened to the injector body 4, the fuel pressure sensingunit U is detachably installed to the injector body 4.

Next, an assembling process of the fuel pressure sensing unit U will bedescribed with reference to FIG. 3.

First of all, the housing 53 is press fitted to the stem 51, to whichthe strain gauge 52 is bonded or joined. Specifically, the fittingsurface portions 51 g, which are formed in the outer peripheral surfaceof the cylindrical tubular portion 51 b of the stem 51, are press fittedto the fitting surface portions 531 b, which are firmed in the innerperipheral surface of the cylindrical tubular portion 53 c of thehousing 53. Thereafter, the spacer 57 and the molded IC device 54 arefixed to the housing 53. Then, the molded IC device 54 is connected tothe strain gauge 52 through the wires W using a bonding machine in thewire bonding process. Next, the case 56 is installed to the housing 53.

The electrodes 71-74 are insert molded with the mold resin 70 m whilethe top surfaces of the connections 71 a-74 a and the sensor terminal 54b side end parts of the electrodes 71-74 are exposed outward from themold resin 70 m. This molded body is placed in a predetermined locationon the top surface of the case 56, and the sensor terminal 54 b side endparts of the electrodes 71-74 are electrically connected to the sensorterminals 54 b through, for example, the laser welding. In this way, theassembling process of the fuel pressure sensing unit U is completed.

Next, an installation process for installing the fuel pressure sensingunit U to the injector body 4 will be described.

First of all, the fuel pressure sensing unit U is installed to theinjector body 4. Specifically, the rotary fastening tool is engaged withand is rotated together with the tool engaging portions 53 d of thehousing 53, so that the housing 53 (thereby the fuel pressure sensingunit U) is rotated. In this way, the male threaded portion 53 e of thehousing 53 is threadably fastened to the female threaded portion 45 a,which is formed in the recess 45 of the injector body 4. Through thethreadably fastening operation, the fuel pressure sensing unit U isinstalled to the injector body 4, and the sensor side seal surface 51 eis urged against the body side seal surface 45 b to generate the axialforce on the seal surfaces 51 e, 45 b, so that the metal-to-metal sealis formed between the seal surfaces 51 e, 45 b.

Prior to the threadably fastening of the housing 53, which securelyholds the stem 51, to the injector body 4, the injector body 4 isprocessed through the quenching process and the carburizing process toharden the surface of the injector body 4. At the time of executing thecarburizing process, a carburization protection is provided to the bodyside seal surface 45 b and the female threaded portion 45 a to protectthe body side seal surface 45 b and the female threaded portion 45 afrom the carburization. For instance, at the time of executing thecarburizing and quenching process, the body side seal surface 45 b andthe female threaded portion 45 a may be masked to limit the hardening ofthe body side seal surface 45 b and the female threaded portion 45 a.Thereby, the rigidity of the body side seal surface 45 b and therigidity of the female threaded portion 45 a become lower than that ofthe rest of the injector body 4.

Next, the drive connector terminals 62 are electrically connected to thelead lines 21. Also, the sensor connector terminals 63 are electricallyconnected to the electrodes 71-74 through the laser welding.

Thereafter, a molding process with mold resin is executed in the statewhere the connector terminals 62, 63 and the fuel pressure sensing unitU are installed to the injector body 4. This mold resin becomes theconnector housing 61 discussed above. In this way, the installation ofthe fuel pressure sensing unit U to the injector body 4 is completed,and the internal electrical connections are made.

Next, there will be described a temperature characteristic test and anabnormality inspection, which are performed on the fuel pressure sensingunit U before the installation of the fuel pressure sensing unit U tothe injector body 4.

When the fuel temperature is increased, the thermal expansiondeformation of the stem 51 is increased. Therefore, the output value ofthe fuel pressure sensor unit U (i.e., the sensor output value outputtedfrom the molded IC device 54) is drifted, i.e., fluctuated. Thereby, thefuel pressure needs to be computed based on the sensor output value inview of the amount of the temperature drift discussed above. The amountof the temperature drift is a specific value, which is specific to, forexample, the stem 51 and the strain gauge 52. Therefore, the amount ofthe temperature drift needs to be obtained in advance throughexperiments before shipment of the injector to the market.

The fuel under the known test temperature and the known test pressure issupplied into the interior of the stem 51 through the flow inlet 51 a,and thereby the pressure of this fuel is applied to the diaphragm 51 c.The amount of the temperature drift for the test temperature is obtainedbased on the sensor output value, the test pressure and the testtemperature of this test time (temperature characteristic test). Acorrection value, which is used to correct the sensor output value, isobtained based on the amount of the temperature drift. Alternatively,the sensor output value may be corrected in situ by using the amount ofthe temperature drift obtained in the above-described manner when theengine is operated upon installation of the injector to the engine.

Furthermore, prior to the shipment of the injector to the market, it maybe checked whether the sensor output value for the test pressure iswithin a normal range. In this way, it is possible to check anabnormality in the strain gauge 52 and the molded IC device 54 alonebefore the installation of the fuel pressure sensing unit U to theinjector body 4. Also, it is possible to check a malfunction at thewelded electrical connections of the sensor terminals 54 b and anelectrical connection malfunction at the connections of the wires W inthe fuel pressure sensing unit U before the installation of the fuelpressure sensing unit U to the injector body 4.

The present embodiment provides the following advantages.

(1) The fuel pressure sensor 50 (including the stem 51 and the straingauge 52), the housing 53, the molded IC device 54, the case 56, thespacer 57 and the electrodes 71-74 are integrally assembled as the fuelpressure sensing unit U, and the housing 53 is threadably fastened tothe injector body 4. In this way, the fuel pressure sensing unit U isinstalled to the injector body 4. Thereby, prior to the installation ofthe stem 51 and the molded IC device 54 to the injector body 4, thetemperature characteristic test and the abnormality inspection can beexecuted on the fuel pressure sensing unit U alone before theinstallation of the fuel pressure sensing unit U to the injector body 4.

Therefore, at the time of executing the above test, the temperatureadjustment may be made to stabilize only the stem 51. Thus, it is notrequired to adjust both of the stem 51 and the injector body 4 to thetest temperature. In this way, the time required for the temperatureadjustment can be shortened, and the work efficiency of the test can beimproved. Furthermore, the above test can be performed on the fuelpressure sensing unit U alone. Therefore, the abnormality in the sensoroutput value can be discovered before the installation of the fuelpressure sensing unit U to the injector body 4. Thereby, it is possibleto avoid the deterioration of the manufacturing yield of the injector.

(2) When the housing 53 is threadably fastened to the injector body 4,the fuel pressure sensing unit U is installed to the injector body 4,and at the same time, the axial force for urging the sensor side sealsurface 51 e and the body side seal surface 45 b toward each other isgenerated. Therefore, the threaded portions 45 a, 53 e can be used forthe purpose of installing the fuel pressure sensing unit U to theinjector body 4 and also for the purpose of generating the axial force.Thus, in comparison to a case where another set of threaded portions isprovided for the purpose of generating the axial force in addition tothe threaded portions for installing the fuel pressure sensing unit tothe injector body, the size of the injector can be reduced. Furthermore,the number of the fastening operations for threadably fastening thethreaded portions together can be reduced, and thereby the productivityof the injector can be improved.

(3) The stem 51 directly contacts the injector body 4 to form themetal-to-metal seal between the stem 51 and the injector body 4.Therefore, the contact location for forming the metal-to-metal seal canbe minimized to the single location. Thereby, the size of the injectorcan be reduced.

(4) The housing 53, which holds the molded IC device 54, is installed tothe stem 51. Therefore, the size of the stem 51 can be reduced incomparison to the case where the molded IC device 54 is held by the stem51. Thereby, the manufacturing costs can be reduced by reducing the sizeof the stem 51, the material costs of which are relatively high.

(5) The housing 53 can be used for the purpose of holding the molded ICdevice 54 and for the purpose of engaging with the rotary fasteningtool. Therefore, the size of the fuel pressure sensing unit U can bereduced.

(6) The fitting surface portions 51 g, which are formed in the outerperipheral surface of the cylindrical tubular portion 51 b of the stem51, are press fitted to the fitting surface portions 531 b, which arefirmed in the inner peripheral surface of the cylindrical tubularportion 53 c of the housing 53. Therefore, the housing 53 can benon-rotatably installed to the stem 51 in the easy way.

(7) The carburization protection is provided to the body side sealsurface 45 b to protect the body side seal surface 45 b from thecarburization at the time of hardening the injector body 4 in thecarburizing process. Therefore, when the sensor side seal surface 51 eis urged against the body side seal surface 45 b to form themetal-to-metal seal, the plastic deformation of the body side sealsurface 45 b can be promoted. Thereby, the contact tightness between thebody side seal surface 45 b and the sensor side seal surface 51 e isimproved to improve the sealing performance of the metal-to-metal seal.When the sealing performance is increased by increasing the fasteningforce for threadably fastening the female threaded portion 45 a and themale threaded portion 53 e together to increase the urging force (axialforce) for urging the stem 51 against the body side seal surface 45 b orby increasing the processing accuracy of the seal surfaces 45 b, 51 e,the manufacturing costs are disadvantageously increased. In contrast,according to the present embodiment, the sealing performance of themetal-to-metal seal can be improved without increasing the axial forceor the processing accuracy.

(8) The carburization protection is provided to the female threadedportion 45 a at the time of hardening the injector body 4 in thecarburizing process. Therefore, it is possible to limit the possibilityof generating a delayed fracture at the female threaded portion 45 a.When the recess 45 is entirely masked, the masking process for maskingthe body side seal surface 45 b and the masking process for masking thefemale threaded portion 45 a can be simultaneously executed. Therefore,the working efficiency can be improved in comparison to a case where themasking process for masking the body side seal surface 45 b and themasking process for masking the female threaded portion 45 a areindividually separately executed.

(9) The sensor side seal surface 51 e is formed at the end surface ofthe cylindrical tubular end part of the stem 51, which is located aroundthe flow inlet 51 a. Specifically, the cylindrical tubular end part ofthe stem 51, which forms the flow inlet 51 a, is used to form the sensorside seal surface 51 e. Therefore, the size of the stem 51 can bereduced.

(10) The stem 51 is formed separately from the injector body 4.Therefore, when the internal stress of the injector body 4, which isgenerated by the thermal expansion or contraction, is conducted to thestem 51, it is possible to increase a conduction loss of such aninternal stress. Specifically, the stem 51 is formed separately from theinjector body 4, so that the influences on the stem 51 caused by thestrain of the injector body 4 is reduced. Therefore, according to thepresent embodiment, in which the strain gauge (sensor element) 52 isinstalled to the stem 51 formed separately from the injector body 4, itis possible to further limit the influences on the strain gauge 52caused by the strain generated in the injector body 4 in comparison to acase where the strain gauge 52 is directly installed to the injectorbody 4.

(11) The material of the stem 51 has the coefficient of thermalexpansion, which is smaller than that of the injector body 4. Therefore,it is possible to limit the generation of the strain on the stem 51caused by the thermal expansion or contraction of the stem 51.Furthermore, in comparison to a case where the entire injector body 4 ismade of the expensive material having the small coefficient of thermalexpansion, it is possible to reduce the material costs since it is onlyrequired to make the stem 51 from the expensive material, which has thesmall coefficient of thermal expansion.

(12) The drive connector terminals 62 and the sensor connector terminals63 are held by the common connector housing 61, so that the driveconnector terminals 62 and the sensor connector terminals 63 are placedin the common connector 60. Therefore, the fuel pressure sensor 50 canbe installed to the injector without increasing the number ofconnector(s). Thereby, the harness, which interconnects between theexternal device (e.g., the engine ECU) and the connector(s), can beextended from the single connector 60, which is provided to the injectorbody 4. Thereby, the placement and connection of the harness can beeasily performed. Also, it is possible to avoid an increase in thenumber of assembling steps for the connector connecting operation.

Second Embodiment

In the first embodiment, as shown in FIG. 4A, the two planar fittingsurface portions 51 g are formed at the outer peripheral surface of thecylindrical tubular portion 51 b of the stem 51, and the two planarfitting surface portions 531 b are formed in the inner peripheralsurface of the cylindrical tubular portion 53 c of the housing 53. Thefitting surface portions 51 g of the stem 51 are press fitted to thefitting surface portions 531 b of the housing 53. In this way, thehousing 53 is non-rotatably installed to the stem 51.

In the second embodiment, as shown in FIG. 4B, knurled grooves (knurledsurface) 510 g are formed in the outer peripheral surface of thecylindrical tubular portion 51 b of the stem 51, and knurled grooves(knurled surface) 530 b are formed in the inner peripheral surface ofthe insertion hole 53 b of the housing 53. The knurled grooves 530 b ofthe housing 53 are press fitted to the knurled grooves 510 g of the stem51, so that the housing 53 is non-rotatably installed to the stem 51.

Alternatively, as shown in FIG. 4C, a plurality (two in this instance)of fixation pins P may be provided. Each fixation pin P is press fittedinto a corresponding gap between the inner peripheral surface of theinsertion hole 531 b of the housing 53 and the outer peripheral surfaceof the cylindrical tubular portion 51 b of the stem 51. In this way, thehousing 53 is non-rotatably installed to the stem 51. Thereby, theadvantages, which are similar to those of the first embodiment, can beachieved.

Third Embodiment

In the first embodiment, when the housing 53 is threadably fastened tothe injector body 4, the sensor side threaded portion 53 e, which isformed in the housing 53, is formed as the male threaded portion, andthe body side threaded portion 45 a, which is formed in the injectorbody 4, is formed as the female threaded portion. In contrast, accordingto the third embodiment, as shown in FIG. 5A or 5B, a sensor sidethreaded portion 530 e, which is formed in the inner peripheral surfaceof the housing 53, is formed as a female threaded portion, and a bodyside threaded portion (not shown), which is formed in an outerperipheral surface of a stub (protrusion) of the injector body 4, isformed as a male threaded portion. The stub of the injector body 4axially protrudes from the rest of the injector body 4, and the branchpassage 6 a extends through the stub to communicate with the flow inlet51 a of the stem 51. The body side seal surface is formed in the topsurface of the stub around the opening of the branch passage 6 a. Thecylindrical tubular portion 53 c of the housing 53 is axially furtherextended from the sensor side seal surface 51 e of the stem 51 towardthe body 4 side, and the female threaded portion 530 e (sensor sidethreaded portion) is formed in the inner peripheral surface of thisextended section of the cylindrical tubular portion 53 c.

Here, as discussed above, in the stem 51, the outer diameter of the oneaxial end part (large diameter part 511 b) of the cylindrical tubularportion 51 b, at which the sensor side seal surface 51 e is formed, islarger than an outer diameter of the other axial end part (smalldiameter part 510 b) of the cylindrical tubular portion 51 b, at whichthe diaphragm 51 c is formed. In the case of FIG. 5A, the large diameterportion 511 b (more specifically, two planar fitting surface portions ofthe large diameter portion 511 b, which are similar to the planarfitting surface portions 51 g of the first embodiment) is press fittedto the inner peripheral surface of the cylindrical tubular portion 53 c(more specifically, two planar fitting surface portions of the innerperipheral surface of the cylindrical tubular portion 53 c, which aresimilar to the planar fitting surface portions 531 b of the firstembodiment) of the housing 53 at a location above the female threadedportion 530 e. Alternatively, in the other example shown in FIG. 5B, thesmall diameter portion 510 b (more specifically, two planar fittingsurface portions of the small diameter portion 510 b, which are similarto the planar fitting surface portions 51 g of the first embodiment) ispress fitted to the inner peripheral surface of the cylindrical tubularportion 53 c (more specifically, two planar fitting surface portions ofthe inner peripheral surface of the cylindrical tubular portion 52 c,which are similar to the planar fitting surface portions 531 b of thefirst embodiment) of the housing 53. Thereby, the advantages, which aresimilar to those of the first embodiment, can be achieved.

The present invention is not limited to the above embodiments, and theabove embodiments may be modified as follows. Furthermore, any one ormore of the features of any one of the embodiments may be combined withany one or more of the features of any other one of the embodiments.

In each of the above embodiments, the stem 51 is press fitted to thehousing 53, so that the housing 53 is non-rotatably installed to thestem 51. Alternatively, the stem 51 and the housing 53 may be joinedtogether by welding. In this way, the housing 53 is non-rotatablyinstalled to the stem 51.

In the first embodiment, the electrodes 71-74, which are integratedtogether with the mold resin 70 m, are provided to the fuel pressuresensing unit U. Alternatively, the electrodes 71-74 may be providedseparately from the fuel pressure sensing unit U. In such a case, at thetime of performing the above-described test and inspection, theelectrodes 71-74 are not yet installed to the fuel pressure sensing unitU.

In each of the above embodiments, the strain gauge 52 is used as thesensor element, which senses the amount of strain on the stem 51.Alternatively, a piezoelectric element or any other suitable sensorelement may be used to sense the amount of strain on the stem 51.

In the first embodiment, the connection 72 a-74 a of each of theelectrodes 72-74, which is connected to the corresponding connectorterminal 63, is configured into the annular form (ring form).Alternatively, the connection 72 a-74 a of each of the electrodes 72-74may be configured into an arcuate form (e.g., a C form). Furthermore, inthe first embodiment, the annular connections 72 a-74 a are placed oneafter another in the radial direction. Alternatively, the annularconnections 72 a-74 a may be placed one after another in the axialdirection.

In each of the above embodiments, the present invention is applied tothe injector that is configured such that the high pressure port 43 isformed in the outer peripheral surface of the injector body 4 to supplythe high pressure fuel from the outer peripheral surface side of theinjector body 4. Alternatively, the present invention may be applied toan injector that is configured such that the high pressure port 43 isformed to the axial side of the injector body 4, which is opposite fromthe injection hole 11 to supply the high pressure fuel from the axialside of the injector body 4.

In each of the above embodiments, the present invention is implementedin the injector of the diesel engine. Alternatively, the presentinvention may be implemented in an injector of a gasoline engine,particularly a direct injection gasoline engine, in which fuel isdirectly injected into the combustion chamber E1.

1. A fuel injection valve being adapted to be installed to an internalcombustion engine and having an injection hole to inject fueltherethrough, the fuel injection valve comprising: a body that includesa high pressure passage, which is adapted to conduct high pressure fueltoward the injection hole; a flexure element that is installed to thebody and is resiliently deformable upon receiving a pressure of the highpressure fuel conducted through the high pressure passage; a sensorelement that is installed to the flexure element to sense a straingenerated in the flexure element, wherein the sensor element convertsthe sensed strain into a corresponding electrical signal; a signalprocessing circuit that executes at least an amplifying operation, whichamplifies the signal received from the sensor element; and a holdingmember that is installed to the flexure element and holds the signalprocessing circuit, wherein: the flexure element, the sensor element,the signal processing circuit and the holding member are integrallyassembled together to form a fuel pressure sensing unit; and the fuelpressure sensing unit is installed to the body by threadably fastening athreaded portion, which is formed at the holding member, to the body. 2.The fuel injection valve according to claim 1, wherein: the flexureelement has a sensor side seal surface, which is urged against the bodyto form a metal-to-metal seal between the sensor side seal surface andthe body; and the sensor side seal surface is urged against the body bya fastening force exerted from the threaded portion of the holdingmember.
 3. The fuel injection valve according to claim 2, wherein: theflexure element is configured into a generally cylindrical hollow bodyhaving a flow inlet at one axial end part thereof and a closed bottom atthe other axial end part thereof; the flow inlet is adapted to pass thehigh pressure fuel therethrough into an interior of the flexure element;and the sensor side seal surface is formed in an end surface of the oneaxial end part of the flexure element around the flow inlet.
 4. The fuelinjection valve according to claim 1, wherein: the flexure element isconfigured into a generally cylindrical hollow body having a flow inletat one axial end part thereof and a closed bottom at the other axial endpart thereof; the flow inlet is adapted to pass the high pressure fueltherethrough into an interior of the flexure element; the closed bottomof the flexure element forms a diaphragm, to which the sensor element isinstalled; the holding member has a receiving portion that receives andholds the signal processing circuit; and an insertion hole is formed inthe receiving portion of the holding member and receives a cylindricaltubular portion of the flexure element therethrough to place thediaphragm in an interior of the receiving portion.
 5. The fuel injectionvalve according to claim 4, wherein: the holding member has acylindrical tubular portion, which is configured into a generallycylindrical tubular body that extends along an outer peripheral surfaceof the flexure element; the receiving portion of the holding memberradially outwardly projects from an outer peripheral surface of thecylindrical tubular portion of the holding member; and the receivingportion of the holding member has a tool engaging portion, which isconfigured to engage with an external rotary fastening tool.
 6. The fuelinjection valve according to claim 4, wherein the holding member isinstalled to and is non-rotatable relative to the flexure element. 7.The fuel injection valve according to claim 6, wherein: the holdingmember has a cylindrical tubular portion, which is configured into agenerally cylindrical tubular body that extends along an outerperipheral surface of the flexure element; and the flexure element ispress fitted to one of an inner peripheral surface of the cylindricaltubular portion of the holding member and the insertion hole of thereceiving portion of the holding member, and thereby the holding memberis installed to and is non-rotatable relative to the flexure element. 8.The fuel injection valve according to claim 1, wherein: the holdingmember has a cylindrical tubular portion, which is configured into agenerally cylindrical tubular body that extends along an outerperipheral surface of the flexure element; and the threaded portion ofthe holding member is formed in one of an outer peripheral surface andan inner peripheral surface of the cylindrical tubular portion of theholding member.